Scientists identify secret ingredient in Leonardo da Vinci's painting

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Leonardo da Vinci and other “ancient masters”, Sandro It has been reported that Botticelli and Rembrandt may have used proteins, specifically egg yolks, in their oil paintings A new study.

Trace protein residues have long been detected in classic oil paintings, although they are usually attributed to contamination. A new study published Tuesday in the journal Nature Communications found that this inclusion was likely intentional and sheds light on the technical knowledge of the Old Masters (the most skilled painters in Europe in the 16th, 17th or early 18th century) and the way they prepared their paints.

Study author Ophélie Ranquet of the Institute of Mechanical Engineering and Mechanics at Karlsruhe Institute of Technology in Germany spoke by phone. “Our results show that using even very small amounts of egg yolk can produce surprising changes in the properties of oil paints, suggesting it may have benefits for artists.”

It turns out that just adding some egg yolk to their creations can have lasting effects that go beyond just being pretty.

Formulated with the ancient Egyptians, it is called Tempera paints combine egg yolks with powdered pigments and water, while oil paints produce richer colors, allow for very smooth color transitions, and dry much more slowly, so they can be used for several days after preparation. However, oil paints that use linseed or safflower oil instead of water have disadvantages, including being more likely to darken and be damaged by exposure to light.

Because making paint was a manual and experimental process, ancient masters may have added egg yolk (a familiar ingredient) to the new paints, which first appeared in Central Asia in the seventh century and then spread to Northern Europe during the Middle Ages and Renaissance period in Italy. In the study, researchers recreated the paint-making process by using four ingredients (egg yolks, distilled water, linseed oil, and pigment) to mix two historically popular and important colors: lead white and ultramarine blue.

“The addition of egg yolk is beneficial because it can greatly adjust the properties of these paints,” says Ranquet, “for example, showing aging in a different way: the paint takes longer to oxidize due to the presence of antioxidants. In the egg yolk ”

The chemical reaction between the oil, pigment and the proteins in the egg yolk directly affects the behavior and viscosity of the paint. “For example, lead white paint is very sensitive to humidity, but if you coat it with a protein layer, it becomes more resistant to humidity, making the paint easy to apply,” Lankai said.

“On the other hand, if you want something harder without having to add a lot of pigment, with a little bit of egg yolk, you can create a thick impasto,” she adds, referring to a method of applying pigments Painting techniques laid out inside. The strokes are thick enough that the strokes are still visible. Lanquet said it would have been desirable to use less pigment centuries ago, when some pigments, such as lapis lazuli used to make ultramarine blue, were more expensive than gold.

Direct evidence of the role, or lack thereof, of egg yolks in oil painting can be seen in Leonardo da Vinci's Madonna of the Carnation, A painting observed during the study. The work is currently on display at the Alte Pinakothek in Munich, Germany. There are obvious wrinkles on the faces of Mary and the child.

“Oil paint dries from the surface, which is why it wrinkles,” Lankai said.

One cause of wrinkling may be an insufficient amount of pigment in the paint, and research shows that this effect can be avoided by adding egg yolk: “This is quite surprising because the amount of pigment in the paint is the same, but the presence of egg yolk changes everything. ”

Because wrinkles appear within days, Leonardo and others are likely Old masters may have noticed this special effect, as well as other beneficial properties of egg yolk in oil painting, including resistance to moisture. Madonna with Carnations is one of Leonardo's earliest paintings, probably created while he was still struggling to master the then-newly popular medium of oil painting.

A new understanding of the classics

Another painting observed during the study was Botticelli's Lamentation of the Dead Christ, also displayed in the Alte Pinakothek. The work is primarily produced in tempera, but oils are also used for the background and some secondary elements.

“We knew that certain parts of the painting showed what we call typical brushstrokes in oil paintings, but we detected the presence of the protein,” Lankai said. “Because the amounts are so small and difficult to detect, this could have been dismissed as contamination: in the workshop, the artist used many different things, and maybe the eggs were just from tempera.”

However, due to the addition of Egg yolk has such a desirable effect on oil painting that the presence of the protein in the work may indicate its intentional use, Research shows. Lanquette hopes these preliminary findings may spark more curiosity about this understudied topic.

Maria Perla Colombini, a professor of analytical chemistry at the University of Pisa in Italy who was not involved in the study, agrees. “This exciting paper provides a new context for understanding ancient painting techniques,” she said in an email.

“The research team reports results from the molecular level to the macroscopic scale, providing new knowledge about the use of egg yolk and oil binders. Instead of simply identifying the materials used by the ancient masters, they explain how they were used as a binder and blending the few available natural materials to produce fantastic and sparkling effects. They try to discover the secrets of old recipes about which little or nothing has been written,” she adds.

“This new knowledge will not only contribute to better conservation and preservation of artworks, but also a better understanding of art history.”

Above: Leonardo da Vinci’s Mona Lisa